Why is water clear?

Answer 1

First of all, let us consider the possible reasons for a material not to be clear - it has to interact with, and disrupt the path of light that hits it. The main reasons are that it may be absorb light (i.e. it may be coloured), it may scatter light, or it may reflect light (There are other, more complex reasons for a substance to be non-transparent, such as frequency doubling properties, but these are the most common).

A substance is coloured if its constituent molecules absorb some wavelengths of visible light. This normally requires an electronic transition, where an electron absorbs electromagnetic radiation and 'jumps' to a higher energy state. This is common in transition metal ions, or in organic compounds with conjugated multiple bonds. If the absorption of light is only weak, a material will be coloured, but if it is strongly absorbed, the material will appear opaque. Water does not have any such transitions.

A substance will tend to scatter light if it comprises different crystalline regions with interfaces (joins) between these regions. Light is diffracted multiple times as it passes through the material, and no straight paths through the material exists for the light. Snow is an example of such a material. Water, as a liquid, cannot have such different regions and so does not display this property.

The reasons why a substance will reflect light are complex, but broadly rely on the existence of a highly conductive and flat surface that prevents an electromagnetic wave from penetrating into the surface of the material. Water is not highly conductive, and so does not show the reflectivity (and so lack of transparency) that we associate with, for example, metals.

In summary, an alternative to the question 'why is water clear' is to ask 'why would water not be clear?' The fact is that there is no significant mechanism, and so no reason, for water to interact with visible light. As a consequence, light passes through it largely unaffected, and so appears clear.

Answer 2

One of the major reasons the Caribbean Sea is so blue is the depth of the water, paired with the bright, light color of the sand. That makes the water so much brighter than other parts of the Ocean, such as the Indian ocean.

Answer 3

beacause the sky is blue there and it reflects on the sea and there is less iron in the sea then the Atlantic Ocean